1. Technical Field
This invention relates generally to capacitive sensors for electronic devices, and more specifically to a device having visible printing adjacent to capacitive sensing devices, where the visible printing does not interfere with the electrical operation of the sensing devices.
2. Background Art
Electronic devices are continually becoming more advanced. The devices are becoming smaller, memories are becoming larger, more features are being added, and processing power is increasing. Some electronic devices today, including personal digital assistants and mobile telephones, have the processing power of a computer, yet still fit easily into a shirt pocket.
One of the advances in electronic device technology involves the user interface. Traditional electronic devices generally included only keys or buttons for data entry. When a user wanted to enter a phone number, for example, the user pressed sequential buttons on the electronic device.
The advent of the touch sensitive display or user input transformed conventional user interface technology. With an electronic device having a touch sensitive surface, rather than pressing keys or buttons, the user is able to interact with the device and enter data by simply placing a finger on a surface of the device. Sometimes the surface will coincide with a device display, thereby transforming a display into a touch sensitive display or screen. Touch sensitive user input devices often simplify the overall appearance of the device as a simple touch sensitive display can eliminate the need for a tethered full keyboard, as the same can sometimes be reproduced as needed in conjunction with the touch sensitive screen.
There are many different touch sensitive technologies. In capacitive sensing technologies, capacitive touch sensors detect the presence of an object, such as a finger or stylus, by determining a changing current flow at the contact point. Exemplary capacitive sensors are taught in, for example, U.S. Pat. Nos. 4,071,691, 4,129,747, 4,198,539, 4,293,734, 4,302,011, 4,371,746, and 4,430,917.
One problem associated with capacitive sensing technologies involves electrical interference. For a capacitive sensor to function properly, an electrical field must be allowed to propagate from one capacitive sensor outside the device and back to another sensor. Any material that interferes with this electrical field can compromise reliability. For example, if the capacitive sensor is placed beneath a protective cover layer having vacuum-metalized printing, the metal in the printing can function as a shield, thereby interfering with the resulting electrical field and inhibiting the operation of the capacitive sensor.
This is a problem because device manufacturers often like to include printing somewhere on the surface of the device. Such printing may indicate to the user the model or manufacturer of the device. Such printing may also include instructions on using the device. Without such printing, the user's ability to operate the device may be slowed or inhibited.
There is thus a need for a method of creating visible printing in an electronic device employing a capacitive sensor, where the printing does not interfere with the electrical operation of the capacitive sensor.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.